Yes Daniel, indeed have heard them on the large Onken loudspeakers with horns, at the 'old' Maison de l'Audiophile in Paris, with William Walther in charge.
And, - Yes, I have tempted to build it for my ESL, but never succeeded far enough (own choice of components, having all bias resistors adjustable till there is a DC equilibrium without feedback applied yet isn't easy). Now I saw the board from the German ebay I might be tempted again to experiment
I do have the 8W (which is not the threads' topic but discussed anyway).
albert

Hi Dan,
here you go:
this is my second implementation with regulated power supply. The first one had passive and in total 12 of those large capacitors.L1007614.jpg

Note the extra large 1 ohm resistors! They still get hot.
I have decoupled the transistors in the cascade stage with solid tantal caps of 27 micro farad.
I have noted that the quality of the feedback set is very important.

what is the power rating of these extra large 1 ohm resistors when you choose to use them without a heatsink?
What is the Rth j-a of the resistor without a heatsink?

Hi Andrew,
these resistors are 50W but in air this is lower. I can't find the thermal resistance in free air - just the derating, which is 35% in such a closed box.
Of course the current is some 750 mA, but the inside of the cabinet reaches easily 35 degrees, and the resistors are some 45 degrees to the touch.
albert